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I have read about placing whitespace in front of scanf but I everything I try does not work. I am trying to read in two sets of three integers. The first scanf works fine while the second does not. I am frustrated because I try everything that I see in forums with placing spaces in front or newline characters and nothing works.

Code in question: 

// Get user input for the two dates:
printf("Enter Date #1 in format mm:dd:yyyy \n");
scanf("%i:%i:%i\n", &D1.month, &D1.day, &D1.year);

printf("Enter Date #2 in format mm:dd:yyyy\n");
scanf("%i:%i:%i", &D2.month, &D2.day, &D2.year);

I tried to put a space AND a newline character in there separatly and together, I tried to read in a dummy variable character to see if that would work. Why can I not enter any data in the second scanf??

The output is shown: 

Enter Date #1 in format mm:dd:yyyy 
09:06:1995
Enter Date #2 in format mm:dd:yyyy
The number of days between 0:1529117256:94769206 and 9:6:1995 is -1783102426

I make a new post because I see explanations with characters but not with integers.

Connor Fuhrman
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    Note that using whitespace characters (such as `\n`) at the end of a `scanf()` format string [causes havoc with interactive input.](https://stackoverflow.com/a/43033218/6879826) – ad absurdum Sep 30 '18 at 22:08
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    Why did you specify that `\n` at the end of the first `scanf` format? What did you try to achieve? – AnT stands with Russia Sep 30 '18 at 22:23
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    Tip: whenever `scanf()` does not act as expected,test the return value from `scanf()` to gain insight. `int cnt = scanf("%i:%i:%i\n", &D1.month, &D1.day, &D1.year); if (cnt != 3) printf("Something amiss %d\n", cnt);` – chux - Reinstate Monica Oct 01 '18 at 02:10

3 Answers3

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When you use %i with scanf:

scanf("%i",&inp);  //INPUT 09 AS MONTH OR ANYTHING

It will read input as octal due the prefixed 0 or leading zero when input is 09, hence the value of inp becomes invalid since 9 is not a valid octal digit, octal digits being 0,1,2,3,4,5,6,7.

Where as in case when %d is being used than 09 input will not be converted into octal and the value read will be 9.

Apart from this there is something I would like to suggest: away-from-scanf

Gaurav
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2

As given in comment (1) by user3121023 changin both to "%d" 's instead of "%i" 's fixed the issue. I am unclear why.

Code is now: 

// Get user input for the two dates:
printf("Enter Date #1 in format mm:dd:yyyy \n");
scanf("%d:%d:%d", &D1.month, &D1.day, &D1.year);

printf("Enter Date #2 in format mm:dd:yyyy\n");
scanf("%d:%d:%d", &D2.month, &D2.day, &D2.year);
Connor Fuhrman
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    "I am unclear why.' (removing `'\n'`) --> Answering the question in [this comment](https://stackoverflow.com/questions/52582254/c-scanf-skipping-second-time#comment92100281_52582254) is the first step. The answer is in [comment](https://stackoverflow.com/questions/52582254/c-scanf-skipping-second-time#comment92100138_52582254) – chux - Reinstate Monica Oct 01 '18 at 02:06
2

In addition:

"%d:%d:%d\n"

would not work. Do not put '\n' in your scanf.

Tycho
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